1. Field of the Invention
This invention relates to an improved fuel cell electrode and the method for manufacturing this electrode.
2. Background Art
Although the idea of generating electricity by the oxidation of gaseous fuel has existed for centuries, an inexpensive, commercially available fuel cell has been heretowith unobtainable. The advantages of fuel cells are well known. The cells are capable of generating large amounts of electricity directly from the reaction of the fuel and the oxidant. Furthermore, unlike conventional lead or alkaline batteries which require replacement of depleted electrode materials, there are no active materials in fuel cell electrodes, giving fuel cells a significantly increased lifetime. The cell only requires recharges of fuel and oxidant to continue operation. Finally, such cells are environmentally sound as they produce only heat, water and small amounts of carbon dioxide as byproducts. The advantages of fuel cells are such that NASA employs hydrogen fuel cells for primary electrical power on satellites and manned space missions. Numerous other applications may be envisioned. For example, inexpensive fuel cells could serve as on site electrical power generators for the power industry, as supplementary power sources for industry through co-generation, as field generators, and as a possible replacement for the internal combustion engine in vehicles.
A fuel cell consists of two chambers, one containing the fuel, usually hydrogen, and the second containing an oxidant, usually oxygen or an oxygen rich gas such as air. The hydrogen and oxidant chambers sandwich two electrodes which in turn surround an electrolyte. Hydrogen atoms are adsorbed at one electrode (the anode) to break the hydrogen molecular bonds, creating hydrogen ions and free electrons. These electrons, as will be discussed, flow from the anode to a load device, such as a light bulb, and flow on to the other electrode, the cathode. The hydrogen ions, migrating through the acidic electrolyte, react with the oxygen molecules at the cathode in a reduction reaction to produce water. The adsorption of the hydrogen molecules is stimulated by the use of a catalyst layer serving as the interface between each of the two electrodes and the electrolyte. The potential difference existing between the hydrogen and oxygen electrodes (anode and cathode, respectively) thus creates an electrical current. Once the electrons reach the cathode, they are consumed by the reduction reaction.
However, current fuel cell electrodes suffer from a number of shortcomings. First, the most efficient known catalyst of hydrogen is platinum, while the most cost effective electrode material is porous carbon. Unfortunately, platinum does not readily adhere to carbon. Thus, the platinum atoms which catalyze the reaction are susceptible to migration from the electrode. Therefore, like a conventional battery, current platinum-based electrodes tend to degrade in performance over time and must be replaced. Second, conventional platinum electrodes are extremely expensive. Due to its normally ordered lattice structure, pure platinum provides only a relatively small surface area of exposed platinum atoms with which to catalyze the oxidation reaction. As a result, in state of the art electrodes, almost 50 grams of platinum is used to produce each kilowatt of electricity. Finally, state of the art fuel cell electrodes which use a solid polymer electrolyte require pre-humidification of the reactant gases because water vapor tends to escape through the pores of the electrode. Loss of water from the solid polymer electrolyte reduces ionic conductivity and the overall cell reaction.
Recently, an exciting advance in the area of electronics and batteries has been the discovery of the C.sub.60 molecule. Until the discovery of this molecule, carbon atoms had been thought to exist in only two molecular states; either in a pyramid shape as in diamond or in a hexagon shape as in graphite. This new carbon molecule contains 60 carbon atoms arranged roughly in a soccer ball shape, prompting the name "buckminster fullerene", "buckyball" or "fullerene." The carbon atoms of the fullerene molecule are bonded in a manner such that there are no dangling surface bonds on the molecule. This molecular configuration has unique properties allowing for ultra stable structures at both the atomic and molecular level, making it ideal for numerous applications. For example, the use of fullerenes for lubricants, semiconductors, and superconductors has been contemplated. Recently, electrical conductivity was found to be maximized by fullerene molecules doped with potassium in such a manner as to form a K.sub.3 C.sub.60 compound. The fullerene salt thus created is a stable metallic crystal which is a completely three dimensional molecular metal formed by potassium atoms arranging themselves within the ordered pattern of fullerenes.
In the context of the present invention, the use of fullerenes in fuel cell electrodes is contemplated as the beneficial advance. Specifically, a fuel electrode must first facilitate the dissolution of gas molecules, then diffusion of the gas molecules to the electrolyte-electrode interface, and finally provide the largest possible area of a material with high electrocatalytic activity in contact with the electrolyte. The use of fullerenes in the composition of fuel cell electrodes will facilitate these functions. In addition, when a solid polymer electrolyte is used, pre-humidification of reactant gases should be unnecessary.